The Hiro H1H (or Navy Type 15) was a 1920s Japanese bomber or reconnaissance biplane flying boat developed from the Felixstowe F.5 by the Hiro Naval Arsenal for the Imperial Japanese Navy. Following licence-production of the Felixstowe F.5 for the Imperial Japanese Navy the company developed an improved version known as the H1H or Navy Type 15. The aircraft was built with three different engine types fitted, the Navy Type 15-1 had longer span upper wings and the Navy Type 15-II had four-bladed propellers. Both the H4H1 and H4H2 remained in front-line naval service through the 1930s.